U.S. patent number 7,355,313 [Application Number 11/306,388] was granted by the patent office on 2008-04-08 for stator, spindle motor, and recording disk driving apparatus.
This patent grant is currently assigned to Nidec Corporation. Invention is credited to Masato Gomyo, Mineo Kurita, Hiromitsu Takamatsu.
United States Patent |
7,355,313 |
Takamatsu , et al. |
April 8, 2008 |
Stator, spindle motor, and recording disk driving apparatus
Abstract
Spindle-motor stator includes at least a first core sheet and at
least one or more second core sheets located next to an end core
sheet. A bent portion bent upward and a protrusion extending upward
from the bent portion are formed at the forward end of the
plurality of the first core sheet. Each of the plurality of teeth
is wound with a conductive wire.
Inventors: |
Takamatsu; Hiromitsu (Kyoto,
JP), Kurita; Mineo (Kyoto, JP), Gomyo;
Masato (Kyoto, JP) |
Assignee: |
Nidec Corporation (Kyoto,
JP)
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Family
ID: |
36739741 |
Appl.
No.: |
11/306,388 |
Filed: |
December 27, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060197401 A1 |
Sep 7, 2006 |
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Foreign Application Priority Data
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Dec 27, 2004 [JP] |
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2004-375292 |
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Current U.S.
Class: |
310/216.016;
310/216.045; 310/216.111; 310/67R |
Current CPC
Class: |
H02K
1/146 (20130101); H02K 21/16 (20130101); H02K
21/22 (20130101) |
Current International
Class: |
H02K
1/00 (20060101) |
Field of
Search: |
;310/216,67R,99,90 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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S61-147765 |
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Jul 1986 |
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JP |
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H04-251541 |
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Sep 1992 |
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JP |
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H11-032466 |
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Feb 1999 |
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JP |
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H11-041891 |
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Feb 1999 |
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JP |
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Primary Examiner: Schuberg; Darren
Assistant Examiner: Nguyen; Hong-Vinh
Attorney, Agent or Firm: Volentine & Whitt, PLLC
Claims
What is claimed is:
1. A stator for use in a motor, said stator comprising: first and
second core sheets stacked in a stacking direction from the first
core sheet to the second core sheet, wherein each of the first and
second core sheets include annular portions which together form an
annular core back, and plurality of teeth portions extending
radially inward from the respective annular portions; and a
conductive wire wound around the teeth portions of the core sheets
to form coils, wherein each of the teeth portions of the first core
sheet is bent such that a radially inward end portion thereof
extends substantially in the stacking direction and traverses
across and beyond a plane of a corresponding teeth portion of the
second core sheet.
2. A stator according to claim 1, wherein the core back is
magnetically connected to the teeth portions.
3. A stator according to claim 2, wherein the teeth portions extend
from the core back substantially perpendicularly to the stacking
direction.
4. A stator according to claim 1, further comprising a third core
sheet stacked on the second core sheet.
5. A stator according to claim 1, wherein the height of the stator
in the stacking direction is 5 mm or less.
6. A spindle motor comprising: the stator as claimed in claim 1; a
rotor having a rotor magnet opposed to the stator; and a bearing
unit operable to support the rotor in a rotatable manner about a
rotation axis; wherein the stacking direction is parallel to the
rotation axis of the rotation of the rotor, and the radially inward
end portion of each of the teeth portions of the first core sheet
is opposed to the rotor magnet in a direction substantially
perpendicular to the rotation axis.
7. A spindle motor according to claim 6, wherein the rotor magnet
is arranged inside the stator in the direction substantially
perpendicular to the rotation axis.
8. A spindle motor according to claim 6, wherein the rotor magnet
is arranged outside the stator in the direction substantially
perpendicular to the rotation axis.
9. A spindle motor according to claim 6, wherein the bearing unit
uses a lubricating oil.
10. A disk drive comprising: the spindle motor as claimed in claim
6; and an access unit operable to perform at least reading
information from and writing information onto a disk capable of
storing the information therein.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a stator, a spindle motor, and a
recording disk driving apparatus, or in particular to a thin
spindle motor.
2. Description of the Related Art
With the recent improvement in the storage capacity density of the
hard disk, demand has increased more and more for a smaller hard
disk drive. Further, applications to the portable devices have
spread. The portable devices are often used in an environment
liable to be subjected to vibrations and shocks, and therefore
required to have a high durability against external forces. An
increased durability against external forces requires an increased
rigidity of the bearing, resulting in an increased bearing friction
loss. On the other hand, a power supply such as a dry cell or a
storage battery not large in power capacity is often used for the
portable devices, and a reduced power consumption is also
required.
FIG. 7 is a longitudinal sectional view showing the structure of a
conventional spindle motor. The spindle motor 100 of FIG. 7
classified as a brushless motor includes a fixed assembly 23 having
a stator 131, a rotor 21 having a rotor magnet 132 and a bearing
22.
The stator 131 includes a plurality of teeth, a core back
magnetically connected to the outer periphery or the inner
periphery of the teeth and a coil wound on each of the teeth. The
teeth and the core back are formed by stacking a plurality of core
sheets molded from a silicon steel sheet high in permeability. The
annular rotor magnet 132 is opposed radially to the teeth.
FIG. 6 shows another example of a conventional spindle motor. In
the spindle motor shown in FIG. 6, the end portion of the uppermost
core sheet 134a opposed to the rotor magnet is bent axially upward.
With this structure, the teeth radially opposed to the rotor magnet
132 have so large an area that the magnetic fluxes of the rotor
magnet 132 can be efficiently utilized. In other words, a large
torque constant is obtained. Even in the case where the current
flowing in the coil 131a is reduced, therefore, a torque equivalent
to the current not reduced in the structure with the core sheet not
bent is obtained, thereby making it possible to reduce the power
consumption.
Nevertheless, several problems are encountered to further reduce
the thickness of this spindle motor 100.
The silicon steel sheet finding wide application as a core sheet is
often formed by pressure rolling and has its own limit of reducing
the thickness. To reduce the thickness of the spindle motor,
therefore, the number of the core sheets stacked is required to be
reduced.
The magnitude of displacement from the ideal angle when the single
core sheet 134a is bent, i.e. the bending margin (D1 in FIG. 6) is
in the range of about 0.5 to 1.5 times the thickness (D2 of FIG. 6)
of a single core sheet.
In the spindle motor shown in FIG. 6, the bending margin D1 of the
core sheet 134 may happen to be radially opposed to the portion of
the rotor magnet 132 having a large magnetic flux density.
In the case of a motor having an axial thickness of less than 10
mm, on the other hand, about two to five core sheets are stacked,
and therefore, the axial height of the bending margin of the core
sheet represents a proportion not negligible of the axial height of
the rotor magnet.
In the bending margin of the core sheet, the radial interval
between the magnet and the plurality of the teeth is larger than
the ideal radial interval between the rotor magnet and the stator.
The force generated by the magnetic interaction is decreased in
inverse proportion to the square of distance. Even in the case
where the core sheet is bent, therefore, the torque constant cannot
be sufficiently improved.
With the decrease in thickness, the core sheet cannot be bent by a
sufficient length and therefore it is difficult to secure the
length of the bent portion.
Further, in the case where the inner peripheral portion of the
teeth is processed after stacking a plurality of core sheets, the
interval between the stacked core sheets may be widened, often
resulting in an uneven thickness of the stator core. Thus, the
axial attraction force of the stator with the motor driven is
changed, with the result that the electromagnetic noises are
occasionally increased or the bearing performance reduced. This
trend is especially conspicuous with a thin spindle motor. Also, in
the case where the spindle motor is mounted on a portable device,
the noises generated are unpleasant to the user, while the lower
bearing performance reduces the driving efficiency and hampers the
longer life of the motor.
BRIEF SUMMARY OF THE INVENTION
A stator as an example of the present invention includes a first
core sheet located at a radial end of the stator, at least one or
more second core sheets located next to the end core sheet, and a
conductive wire wound on each of a plurality of teeth.
The stator is laminated by the first core sheet and the second core
sheets, and the stator has the plurality of teeth extending in
radial direction.
The first core sheet has a bent portion bent in axial direction
from the first core sheet to the second core sheets at the forward
end and the first core sheet has a protrusion at the tip of the
bent portion.
According to the present invention, there is also provided a
high-efficiency stator and a spindle motor including this
stator.
Also, according to the invention, there is provided a small, thin
stator and a spindle motor including this stator.
This invention is applicable also to a recording disk driving
apparatus satisfying the recent demand for small thickness and
small power consumption.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 is a longitudinal sectional view showing a hard disk drive
using a spindle motor according to a first embodiment of the
invention.
FIG. 2 is a longitudinal sectional view showing the spindle motor
according to the first embodiment of the invention.
FIG. 3 is a plan view showing a stator and a rotor magnet of the
spindle motor shown in FIG. 1.
FIG. 4 is a longitudinal sectional view showing a spindle motor
according to a second embodiment of the invention.
FIG. 5 is a longitudinal sectional view showing a spindle motor
according to a third embodiment of the invention.
FIG. 6 is a longitudinal sectional view of a conventional spindle
motor.
FIG. 7 is a longitudinal sectional view of a conventional spindle
motor.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIGS. 1 to 5, an embodiment of the invention is
explained. In the description of the invention, the relative
positions and the four directions of the members described herein
are those as viewed in the drawings but not those in which the
members are actually built in the devices.
First Embodiment
FIG. 1 shows a hard disk driving apparatus having a spindle motor 3
according to the invention. The hard disk driving apparatus 1 using
the spindle motor 3 according to the invention includes a housing
12 forming an internal space. The housing 12 has arranged therein
the spindle motor 3, a hard disk (recording disk) 11 in which
information can be recorded, and an access unit having a head 13
for reading/writing information on the disk and a head assembly 14
for supporting and moving the head 13 to an arbitrary position on
the disk.
FIG. 2 is a longitudinal sectional view including the center axis
of the spindle motor 3 according to the invention. The spindle
motor 3 includes a rotor hub 21 having a surface on which the hard
disk 11 is mounted, a base plate 23 forming a part of the housing
12 and a bearing 22 for rotatably supporting the rotor hub 21.
The bearing 22 is a slide bearing including a shaft, a sleeve
fitted in the gap of the shaft and a lubricating oil interposed
between the shaft and the sleeve. The slide bearing may be a
dynamic bearing with a dynamic pressure groove formed in the shaft
and the sleeve, or a roll bearing configured of a rotary member
(ball or cylindrical member) between outer and inner rings.
FIG. 2 is a longitudinal sectional view showing a stator 31 and a
rotor magnet 32 constituting the essential parts of the spindle
motor according to the invention. FIG. 3 is a plan view, taken from
above in FIG. 2, showing the stator 31 and the rotor magnet 32
constituting the essential parts of the invention. In FIG. 3, the
conductive wires 31a are shown by dashed lines and partly omitted
for the convenience of explaining the stator core 33.
The stator core 33 includes an annular core back 33a located on the
outer periphery of the stator 31, and a plurality of teeth 33b
connected magnetically with the core back 33a and extending
radially inward from the core back 33a while being radially
arranged around the center axis thereof. The stator core 33
includes two core sheets 34a, 34b. The second core sheet 34a is
stacked on the upper surface of the first core sheet 34b. The first
core sheet 34b and the second core sheet 34a each includes an
annular core back piece and a plurality of teeth pieces extending
radially inward from the core back piece. The stator core 33 is an
assembly in which the second core sheet 34a is stacked on the upper
surface of the first core sheet 34b.
An protrusion 34b1 is formed at the inner peripheral end (forward
end) of the first core sheet 34b. The outer peripheral surface of
the protrusion 34b1 is arranged radially inward of the inner
peripheral end of the second core sheet 34a, and the inner
peripheral surface of the protrusion 34b1 is opposed to the outer
peripheral surface of the radially magnetized rotor magnet 32 with
a radial gap therebetween. The upper end of the protrusion 34b1 is
projected axially upward from the upper end surface of the second
core sheet 34a.
A bent portion 34b3 having the same height as the axial height of
the bending margin is formed under the protrusion 34b1. The bent
portion 34b3 is upwardly bent from the inner peripheral end of the
first core sheet 34b. The protrusion 34b1, the bent portion 34b3,
and the first core sheet 34b are seamlessly formed with one
component. A part of the bent portion 34b3 is radially opposed to
the rotor magnet 32. The radial gap between the bent portion 34b3
and the outer peripheral surface of the rotor magnet 32 is larger
than that between the inner peripheral surface of the protrusion
34b1 and the rotor magnet 32. Therefore, the bent portion 34b3, as
compared with the protrusion 34b1, has a small magnetic interaction
with the rotor magnet 32. In view of the fact that only a part of
the bent portion 34b3 is opposed to the rotor magnet 32, the torque
reduction can be suppressed more than in the prior art in which the
whole bent portion is opposed to the rotor magnet.
Also, the bent portion 34b3 is not opposed to the center of the
magnetic pole of the rotor magnet 32, and therefore the effective
area of the opposed surfaces of the stator 31 and the rotor magnet
32 can be increased. As a result, the torque constant can be
increased thereby improving the motor efficiency.
This invention finds suitable application especially to implement a
thin spindle motor having an axial thickness of not more than 10 mm
(more preferably, not more than 5 mm). Such a motor has few core
sheets in stack and therefore the ratio which the bending margin of
the core sheet represents of the axial height of the stator core is
large. As a result, this invention can increase the faced areas of
the rotor magnet and the teeth.
Also, according to the first embodiment, the area of the portion of
the stator effectively opposed to the rotor magnet can be increased
within the portion of the rotor magnet having a large magnetic
flux. Thus, the high-efficiency spindle motor can be reduced in
thickness.
According to the first embodiment, the axial thickness of the first
core sheet 34b and the second core sheet 34a is about 0.2 mm, and
the stator core 33 is formed of two core sheets. The axial height
of the rotor magnet 32 is about 0.7 mm, and the axial height of the
protrusion 34b1 including the bending margin is about 0.6 mm. The
thickness of the bending margin, on the other hand, is
substantially the same 0.2 mm as the axial thickness of the single
core sheet. According to this embodiment, the axial center of the
stator core 33 defined as an axially intermediate position of the
two core sheets is located about 0.1 mm downward from the axial
center of the rotor magnet 32.
Also, with regard to the conventional spindle motor 100 shown in
FIG. 6, an experiment is conducted under similar conditions to the
first embodiment including the axial thickness of each of the two
core sheets, the axial height of the rotor magnet 132, the radial
thickness of the protrusion and the size of the bending margin.
Further, with regard to the spindle motor 100 shown in FIG. 7, an
experiment is conducted under similar conditions to the first
embodiment including the axial thickness of the two core sheets
134a, 134b and the axial height of the rotor magnet 132.
As a result, the torque constant of the spindle motor 3 according
to this embodiment is found to be 11% higher than the conventional
spindle motor shown in FIG. 7 and about 3% higher than the
conventional spindle motor shown in FIG. 6.
In the conventional motor shown in FIG. 6, the axial height of the
stator 131 radially opposed to the rotor magnet 132 is dependent on
the accuracy of the parts of the stator 131. In the prior art, the
accuracy of the parts of the stator 131 is determined by the total
of the variations of the length by which the core sheet is bent and
the variations in stacking the core sheets.
According to the first embodiment, on the other hand, the parts
accuracy of the stator is determined only by the bending length of
the protrusion 34b1 of the first core sheet 34b. As a result, the
magnetic flux amount of the stator 31 is stabilized, while at the
same time improving the axial position accuracy of the stator 31
and the rotor magnet 32.
Especially with the thin motor as in this embodiment, a slight
dimensional error causes an imbalance of the axial magnetic force,
and the motor characteristics are greatly affected by the
generation of magnetic noises and an excessive pilot pressure in
axial direction. In the spindle motor 3 according to this
embodiment, therefore, though very thin, individual differences are
small and stable characteristics are obtained.
Further, when the inner diameter of the stator 31 is processed, the
interval between the first and second core sheets is not axially
widened. As a result, the variations in axial thickness of the
stator core 33 are greatly reduced, so that the reduction in the
bearing performance attributable to the variations of magnetic
attraction force or the generation of electromagnetic noises can be
suppressed. The provision of this spindle motor 3 secures the
stable performance and quietude of the hard disk driving apparatus
1.
Second Embodiment
FIG. 4 is a longitudinal sectional view showing a second embodiment
of the invention. As shown in FIG. 4, the stator core 231 includes
a second core sheet 34a and a first core sheet 34b stacked on the
upper side of the second core sheet 34a. The inner peripheral end
of the teeth pieces of the first core sheet 234b is formed with a
downwardly bent protrusion 234b1. The inner peripheral surface of
the protrusion 234b1 is faced with the outer peripheral surface of
the radially magnetized rotor magnet 232. Also, the upper side of
the protrusion as viewed in FIG. 4 is formed with a bent portion
234b3.
With the configuration shown in FIG. 4, the second embodiment can
produce similar operational effects to the first embodiment.
Third Embodiment
FIG. 5 is a longitudinal sectional view showing a third embodiment
of the invention. The spindle motor shown in FIG. 5 has a rotor
magnet 332 arranged radially outward of the stator 331.
As shown in FIG. 5, the stator 331 includes a first core sheet
334b, a second core sheet 334a stacked on the upper side of the
first core sheet 334a, and a third core sheet 334c stacked on the
upper side of the second core sheet 334a. The inner peripheral end
of the teeth pieces of the first core sheet 334b is formed with an
upwardly bent protrusion 334b1. The outer peripheral surface of the
protrusion 334b1 is faced with the inner peripheral surface of the
radially magnetized rotor magnet 332. Also, a bent portion 334b3 is
formed on the lower side of the protrusion 334b1 as viewed in FIG.
5.
The axial height of the protrusion 334b1 including the bending
margin is extended upward from the upper end surface of the third
core sheet 334c. Further, the axial height of the protrusion 334b1
excluding the bending margin is preferably extended upward from the
upper end surface of the third core sheet 334c.
As described above, the spindle motor having the stator 331
arranged radially inward of the rotor magnet is applicable in the
invention. The spindle motor according to the first and second
embodiments described above is suitably reduced in thickness and
has a smaller rotary member. Especially, therefore, the invention
produces the conspicuous effect to reduce the size of the spindle
motor. In the spindle motor according to the third embodiment, on
the other hand, the rotor magnet is covered by a substantially
cup-shaped rotor hub molded from a magnetic material, and therefore
the leakage magnetic fluxes are prevented. This is especially
effective for the motor requiring a high torque.
This invention is applicable also to the structure in which three
core sheets are stacked.
The stator, the spindle motor, and the recording disk driving
apparatus according to the embodiments of the present invention are
described above. The present invention, however, is not limited to
those embodiments, but can be variously modified or altered without
departing from the scope of the invention.
For example, the material of the core sheet may be silicon steel,
ferrite, iron-group amorphus, cobalt or nickel or a similar
ferromagnetic material. Also, the first core sheet and the second
core sheet may be formed of different materials from each
other.
The surface of the protrusion faced to the rotor magnet is not
necessarily a peripheral surface. Specifically, the protrusion
surface may be an arcuate surface corresponding to the peripheral
surface of the rotor magnet or may have other shapes corresponding
to the magnetization waveform or shape of the rotor magnet.
Also, this invention is applicable to the stator having a stack of
two or more core sheets.
* * * * *